While it has been hypothesized that mental illness, including mood disorders such as major depression and bipolar disorder as well as psychotic disorders such as psychosis and schizophrenia, may have genetic roots, little progress has been made in identifying gene sequences and gene products that play a role in causing these disorders, as is true for many diseases with a complex genetic origin (see, e.g., Burmeister, Biol. Psychiatry 45:522-532 (1999)). Relying on the discovery that certain genes expressed in particular brain pathways and regions are likely involved in the development of mental illness, the present invention provides methods for diagnosis and treatment of mental illness, as well as methods for identifying compounds effective in treating mental illness.